DESCRIPTION (Applicant?s abstract): Although the murine Local Lymph Node Assay (LLNA) is effective at detecting potential irritants/sensitizers, this assay, in its current standard form: 1) cannot readily differentiate some types of irritants from respiratory and contact sensitizers; 2) utilizes moderate amounts of radioactive material and; 3) requires increased numbers of animals to determine the different endpoints (i.e., proliferation, immunophenotype) to fully characterize the response of an animal to a topically-applied chemical. To enhance and improve this important test, our company has implemented several innovative modifications to the standard LLNA. We have applied flow cytometric techniques to this assay to increase the sensitivity/specificity of the assay, eliminate the use of radioactive material and decrease the number of animals used for screening. It has been determined by the results of SBIR Phase I studies that the proposed enhanced flow cytometry-based LLNA is technically and commercially feasible. However, to develop this assay to its full commercial potential, which our company would provide to the chemical, pharmaceutical and consumer products industries, our group must: 1) validate the enhanced version of the LLNA; 2) establish the cytometry-based LLNA as a GLP compliant assay at our company and; 3) develop and provide various versions of the enhanced LLNA for our clients.